A fuel injection control device controls injection through a fuel injection valve of an electromagnetically driven type incorporated in an internal combustion engine. Specifically, a fuel injection control device calculates a requested injection quantity in response to the operational status of an internal combustion engine and conducts a coil by an injection command pulse of a pulse width corresponding to the requested injection quantity. As a result, a magnetic attraction force is generated in the coil, a valve body of a fuel injection valve is driven to valve opening, and a fuel is controlled so as to be injected by the requested injection quantity.
In a fuel injection valve of a direct-injection type that injects a fuel of a high pressure directly into a cylinder however, the linearity of the change characteristic of an actual injection quantity to the pulse width of an injection command pulse tends to deteriorate in a partial lift region. The partial lift region means a region of a partial lift state where an injection command pulse width is short and the lift quantity of a valve body does not reach a full lift position. In such a partial lift region, the variation of the lift quantity of a valve body increases and the variation of an injection quantity tends to increase. If the variation of an injection quantity increases, exhaust emission and drivability may deteriorate undesirably.
In a partial lift region, the variation of the lift quantity of a valve body is large and hence the variation of time from the start of valve closing to the finish of the valve closing is also large. When the timing of valve closing by a valve body can be detected in a partial lift region however, deviation between an injection command pulse from a fuel injection control device and actual valve behavior can be recognized by the fuel injection control device. Consequently, it is possible to correct an injection command pulse on the basis of the deviation and control an injection quantity. A technology of detecting the timing of valve closing is disclosed accordingly.
In a fuel injection valve, an induced electromotive force is generated in a coil in proportion to the displacement of a valve body after an injection command pulse is turned off. Since a terminal voltage of the fuel injection valve varies by the generated induced electromotive force therefore, the induced electromotive force can be detected. Two modes of detecting the timing of valve closing by using such an induced electromotive force generated in a coil are disclosed. In Patent Literature 1, as the detection of an induced electromotive force quantity, the difference of an induced electromotive force quantity generated during valve closing caused by the difference of a lift quantity is detected. In Patent Literature 2, as timing detection, an inflection point of an induced electromotive force responding to the drive variation of a movable core after a valve body is seated is detected by using a terminal voltage.